What version of cPanel are you running? Also, if it's 10.6.x what do you have set in WHM > Tweak Settings > The maximum memory a cPanel process can use before it is killed off. It should be at least 64, ideally 128. Also, do you have PRM installed? If so, try disabling it or excluding cpsrvd from it. Finally, check the error log in /usr/local/cpanel/logs/error_log